Prior research on the effects of psychotropic drugs/substances upon performance has most often been guided by concerns with safety and, cognitive effort. Human functioning in the work place, however, includes a large proportion of complex cognitive efforts that have not been adequately captured by prior research. Experimentally based knowledge of psychotropic substance effects upon performance is especially limited for white collar occupations. Previously, the ability to assess substance effects upon complex cognitive functioning and complex task performance has been restricted by the absence of appropriate laboratory based measures. However, a relevant quasi-experimental simulation with continuous control over independent variable manipulations is now available. Reliability and validity (i.e., multiple prediction of success at the work place) for this technique are excellent. The simulation methodology permits the collection of performance data that are based on a range of cognitive efforts, reflecting simple, intermediate and several complex aspects of task performance. The methodology has been used previously to measure the effects of prescription medications on performance. The proposed research will employ this simulation methodology (and several other measurement techniques that have been previously employed to assess effects of psychotropic drugs on simple and intermediate performance) to obtain information about the effects of four substances upon functioning in job settings. The research will employ a placebo controlled double- blind cross-over design. Four substances and, in addition, three combinations of two of these substances at several dosage levels will be included: Marijuana, caffeine, diazepam and alcohol. Participants will be healthy males who have been prior users of these substances, aged 21 through 45 (35 in the case of marijuana). Blood levels will be assayed. The research was designed to help clarify the effects of the four substances on (especially complex) task performance, to elucidate the relationship between blood levels and complex performance, to determine the effects of substances dosage upon complex performance and to obtain information on potential parallel substance effects upon different kinds (or levels) of performance that would require diverse cognitive efforts. The obtained results should aid in the advancement of existing theoretical positions, in the development of hypotheses that are specifically relevant to psychotropic substance impact on complex performance, and in the development of new theory within that domain. Obtained data should also be useful for public relations campaigns that are intended to dissuade white collar employees from using psychotropic substances.